Life Cycle Assessment Of Microalgae Biodiesel Based On Microalgae Climatic-Growth Model

Compared with traditional terrestrial biomass materials,the microalgae have lots of advantages including:rapid growth rate,high oil content and no occupation of farmland.Using microalgae as raw material to produce vehicle fuels is gaining widespread attention due to its positive effect on solving the shortage of fossil fuels and intensifying the greenhouse effect.As a common microalgae culture system,the open race pond?ORP?is regarded as a feasible system for the large-scale,low cost microalgae biodiesel production because of its simple structure,low operation cost and high net energy ration?NER>1?.Currently,a series of life cycle assessment?LCA?studies on microalgae biodiesel produced by ORP have been evaluated and published by researchers all over the world.However there are some limitations in existing studies.On the one hand,produce microalgae by ORP is susceptible to the temperature,lights,as well as other factors.Thus the microalgae yield per unit area fluctuates greatly with climate and seasonal changes.However the existing LCA studies are mainly based on extrapolations from laboratory experiments and usually regard the microalgae yield as a constant value rather than a variable,ignoring the impact of external environmental factors on LCA results;On the other hand,produce microalgae by ORP will consume lots of water resource,but few researches are concerning about the water consumption during microalgae biodiesel production.Therefore,in order to quantify the resources consumption?including water?and the green house gas?GHG?emission during microalgae production.Based on the climate-growth model of microalgae,this research evaluated a LCA study on microalgae biodiesel produced by OPR system.The main research contents of this thesis are as follow:Firstly,based on the climate-growth model of microalgae as well as the meteorological data,the maximum yield and the theoretical yield of microalgae per unit area in Hangzhou,Weihai,Haikou and Wuhan were estimated on a monthly basis.The result show that:Both the maximum and theoretical yield of microalgae per unit area are significantly influenced by the seasonal changes,and show the tendency increasing at the beginning and declining in late within a year.The theoretical yield of microalgae in four regions in different months are between 0³4g/m2/day,which is much lower than the corresponding maximum yield due to the effect of light saturation effect and the unsuitable temperature.Secondly,according to the feasible microalgae biodiesel production process this research established a complete ORP microalgae biodiesel production system.This microalgae biodiesel production system contains a serious of processes including:microalgae cultivation process,algae dewatering process,homogenization process,oil extraction process and transesterification process.The total area of race ponds in this system is 100 hectares.The result shows that produce 1ton of microalgae biodiesel require consumption of 5.98 tons of microalgae raw material.Two main byproducts including 3.57tons of defatted algae residue and 0.1ton glycerol are also been produced during production process.The result also shows that the annual operation time of this ORP biodiesel production system is greatly affected by the water temperature.Within four systems,only the system that located in Haikou region can uninterrupted operate throughout the year.Therefore,it is desirable to install such systems in the tropics area to achieve high annual production efficiency.Finally based on the monthly theoretical yield of microalgae of each region,which had already been obtained,the life cycle assessment was performed.Finally,this research analyzed the life cycle energy consumption,emissions and water footprint of biodiesel produced by this systems.In terms of energy consumption and emissions,The life cycle fossil energy consumption and the GHG emissions per ton of biodiesel could reaches101952.9 MJ/ton and 10226.3 kgCO_2eq/ton respectively when the yield of biodiesel produced by this systems equal to 3ton/day.Meanwhile,the utilization of byproducts could create huge energy and GHG credits for the system,which is enough to offset the petroleum usage and GHG emissions during biodiesel production process.Therefore we conclude that the by-product produced in the microalgae production process should be fully utilized to improve the LCA performance of biodiesel;In terms of water footprint,the result shows that:The water demand and the biodiesel life-cycle water footprint produced by this system will greatly affected by regional and seasonal changes.Within above four systems,the microalgae biodiesel produced by Wuhan system has the highest annual average life cycle water footprint,and the life cycle footprint of microalgae biodiesel produced by this system in different months range from 2621 to 6020 m3/ton.The grey water footprint is the largest component of life cycle water footprint,which account for more than 50%share for every system in every months.